1. Technical Field
The present invention relates to a resonator element, a resonator, an oscillator, an electronic apparatus, a sensor, and a mobile object.
2. Related Art
For example, in a small information apparatus such as a hard disk drive (HDD), a mobile computer or an IC card, or in a mobile object communication apparatus such as a mobile phone, a car phone or a paging system, an electronic device such as a resonator or an oscillator is widely used.
A general resonator element used in such an electronic device includes a base, and a pair of vibrating arms that extends from the base. Such a resonator element is normally obtained by etching a wafer made of quartz crystal or the like to form an appearance with a part of the base being connected to a base material through a breaking portion, and then, by breaking the breaking portion.
For example, in a resonator element disclosed in JP-A-2010-278831, a breaking portion is disposed in an end portion of a base on a side opposite to a vibrating arm. Further, in a resonator element disclosed in JP-A-2008-177723, a breaking portion is disposed in both end portions of a base in a direction where a pair of vibrating arms is arranged.
Recently, as miniaturization of various apparatuses provided with such a resonator element, miniaturization of the resonator element is also requested as much as possible. Particularly, it is desirable to shorten the length of the resonator element along a direction where the vibrating arms extend.
However, in the resonator elements disclosed in JP-A-2010-278831 and JP-A-2008-177723, it is difficult to achieve sufficient miniaturization, and if the length of the base in the extension direction of the vibrating arms is simply shortened, thermoelastic loss increases.
Particularly, in the resonator element disclosed in JP-A-2010-278831, since a concave portion is formed in the vicinity of a root of the breaking portion of the base, if the length of the base along the extension direction of the vibrating arms is shortened, a portion where the length of the base is shortened more than necessary due to the presence of the concave portion is formed, and consequently, the thermoelastic loss increases. The reason is as follows: That is, the base having the length shortened along the extension direction of the vibrating arms performs flexural vibration when the pair of vibrating arms performs flexural vibration, deformation of extension and contraction or contraction and extension occurs in a peripheral region of one end portion where the vibrating arms are connected and in a peripheral region of the other end portion opposite to the one end portion, and thus, a temperature decrease occurs in a region where the extension occurs and a temperature increase occurs in a region where the contraction occurs. Thus, energy capable of being mechanically used is reduced due to heat flow caused due to a temperature difference. Further, in the resonator element disclosed in JP-A-2010-278831, if the length of the base along the extension direction of the vibrating arms is shortened, when the vibrating arms perform the flexural vibration, distortion is concentrated on the concave portion, and accordingly, heat flow increases due to increase of a temperature change of the base. Consequently, the thermoelastic loss also increases. In addition, in the resonator element disclosed in JP-A-2010-278831, if the length of the base along the extension direction of the vibrating arms is shortened, when shock is applied from the outside, stress concentrates on the concave portion, which may be a starting point of breakage.